This invention relates to load break disconnecting switches which are used with transformers and more particularly with housed, ground-level mounted transformers employed with underground distributions systems.
Electrical distribution systems are typically buried underground for reasons of aesthetics, safety and system longevity. The step down distribution transformers employed in such distribution systems must be accessible, however, so that they are generally mounted on a ground-level concrete pad and are enclosed within a metallic housing. It is preferable that these housings are as compact as possible, not only so that they will be inconspicuous, but also for reasons of economy and safety. As a result, conventional load break disconnecting switches and fuses, which are designed for use and installations where space is not a particular problem, have been found unsatisfactory for use with underground systems.
Loadbreak disconnecting switches and fuses are mounted between upper and lower insulators with the upper insulator having a stationary contact jaw and the lower insulator supporting a hinge member. The distance between the upper stationary contact jaw and the lower hinge member is a standard distance in the industry. To avoid replacing the mounting to install a new loadbreak disconnecting device, it is preferred that the loadbreak disconnecting device have dimensions and features which allow it to be used with conventional insulator mountings.
U.S. Pat. No. 3,235,696 to Mikulecky discloses a typical prior art load break disconnecting device. The load break disconnecting device of Mikulecky is a nonconductive means mounted on an elongate switch means and is resiliently urged into covering relation of a conductive portion of the switch means relative to stationary contact means upon movement of the switch means away from the stationary contact means so that any arc struck therebetween will be extinguished. The nonconductive means is a sleeve concentrically mounted on the switch means for longitudinal movement toward a covering relation with respect to the conductive portion. The switch means includes a spring latch means for holding the nonconductive means away from the conductive portion and the stationary contact means includes a latch release means so that the nonconductive means is released upon movement of the switch means into and subsequently out of engagement with the stationary contact means. The load interrupting device cannot be closed until its interrupting structure is relatched. The conductive means may include a fuse having a fusible element wound around a support rod of an insulating material. Such fuses are of the gassing type which are shorter in length than non-gassing type fuses.